Vol 40, No 3 (2024)
Thermohydrodynamics of the ocean and the atmosphere
Finite-difference approximation of the potential vorticity equation for a stratified incompressible fluid and an example of its application for modeling the Black Sea circulation. Part II. Discrete equation of potential vorticity in a quasi-static approximation and an example of its application for simulation the Black Sea circulation in 2011
Abstract
Purpose. The study is purposed at deriving a finite-difference equation of potential vorticity for a three-dimensional baroclinic fluid with regard for diffusion and viscosity in a quasi-static approximation. Its terms are calculated and analyzed in numerical modeling of the Black Sea circulation for two periods – winter and summer 2011.
Methods and Results. A finite-difference equation for the potential vorticity of a stratified incompressible fluid is obtained for a system of discrete equations of sea dynamics in the hydrostatic approximation allowing for viscosity, diffusion, river inflow, water exchange through the straits and atmospheric forcing. It is shown that the main contribution to the potential vorticity is made by its vertical component. The horizontal components are predominant in the areas of river inflow and water exchange through the straits. The vertical component of potential vorticity, except for the river inflow zones, is conditioned by the magnitude and structure of an absolute eddy. The main contribution in the sea upper layer of the coastal region, its northwestern part and along the Anatolian coast is made by the advection of potential vorticity. At the lower horizons, its highest values are observed in the coastal strip, at that its character is more pronounced near the southern coast of the sea.
Conclusions. Analysis of the potential vorticity equation has shown that the value of the advective terms is conditioned by the divergence of the product of nonlinear terms in the motion equations and density gradient. The main conclusion consists in the following: locally, the sum of vertical and horizontal advection of potential vorticity is two orders of magnitude less than each of them separately.
353-370
Analysis of observations and methods of calculating Hydrophysical fields in the ocean
Errors in calculating density using the CTD probe data in suboxic layer of the Black Sea
Abstract
Purpose. The purpose of this work is to study the density of water in two ways in the suboxiс layer of the Black Sea, to assess errors in calculating density using a standard method based on hydrophysical equipment data, to compare the results obtained with other characteristics of sea waters and to analyze the causes of these errors.
Methods and Results. The waters of the Black Sea suboxiс layer were studied in May 2021 and October 2022. Water density was measured with a high-precision laboratory density meter and calculated from the CTD probe data using electrical conductivity by the EOS-80 equation of state. The turbidity values were measured by a turbidimeter while sampling. The concentrations of major ions of the major ion-salt composition in the studied samples were determined by a potentiometric titration, and their difference from the standard sea water IAPSO was assessed in the laboratory. The assessing procedure showed that, as compared to the standard sea water, the contents of and were higher on average by 0.2 and 0.6%, respectively, both K+ and Ca2+ – by 0.2% , and the contents of Clˉ and Na+ were lower on average by 0.4 and 0.3%, respectively. The content of Mg2+ was close to its content in standard sea water. It was found that within the range of conditional density (σt) 15.9−16.2 kg/m3, the vertical distribution of major ions was not linear, especially in relation to chlorides and sulfates.
Conclusions. As a result of determining the density of the waters of the suboxiс layer of the Black Sea in two ways and comparing the obtained values, it was found that the errors in calculating the density according to the CTD probe data amount to 0.05–0.2 kg/m3 and are due to variations in the ion-salt composition and the presence of a large suspension concentrations. The density gradient measured by a density meter is approximately twice as large as that measured by a CTD probe.
371-385
Trends in the interannual variability of salinity field in the upper 1000-meter layer of the northeastern Pacific Ocean under conditions of modern global warming
Abstract
Purpose. The study is purposed at determining the trends and the regional features of interannual changes in salinity and salt content in the upper 1000-m layer of the extratropical zone in the northeastern Pacific Ocean, and at analyzing their possible cause-and-effect relations with the large-scale and regional processes in the ocean and atmosphere over the last two decades of the current period of global warming.
Methods and Results. The NOAA climate data sets including the GODAS oceanographic data assimilation system in the nodes of a regular grid, as well as the data on the amount of atmospheric precipitation and the series of climate indices were used in the study. The monthly average ERA5 reanalysis data on precipitation and evaporation from the underlying surface were also applied. The methods of cluster, correlation and regression analysis, as well as the apparatus of empirical orthogonal functions were involved. The conducted research resulted in identifying the regional spatial and temporal features of the changes in salinity and salt content in the upper 1000-m water column of the study area under conditions of the current warming phase accompanied by the intensification of global and local hydrological cycles. The quantitative characteristics of the noted trends and their statistical significance were assessed.
Conclusions. The spatial distribution of evaporation-precipitation (E-P) difference trends demonstrates a predominant evaporation pattern over most of the water area that differs from the global trends in a hydrological cycle in the middle and high latitudes of the Northern Hemisphere, especially over the previous period. In general, a statistically significant positive trend in salt content was observed in the upper 1000 m of water column in the northern area, whereas in the other regions and on the average over the whole water area, small statistically insignificant negative trends were noted in the above mentioned layer. The correlation relations between the changes in average annual salinity and salt content values, on the one hand, and different large-scale regional processes and climate variables, on the other hand, are most manifested through the following parameters: climate indices NPGO, IPO, PDO and AD, the first mode of EOF of fluctuations in the PC1 values of evaporation-precipitation (E-P) difference, and the second mode of EOF of anomaly of the isobaric surface AT500 geopotential.
386-401
Comparison analysis of heat and mass transport through Fram Strait calculated using the mooring and ocean reanalysis data
Abstract
Purpose. The paper represents a comparison analysis of water, heat and salt flows transported through Fram Strait and calculated using the data both of moorings in the strait and the GLORYS2v4, ORAS5, GloSea5 and C-GLORSv7 reanalysis.
Methods and Results. The data obtained at the autonomous buoy stations were interpolated in the nodes of a regular grid with the resolutions 0.25° over longitude and 10 m over depth using the Ordinary Kriging. The algorithms unified both for the mooring and reanalysis data were applied to calculate the transport flows in 1997–2018. The data of moorings and reanalysis constituted a base for obtaining the time series of heat and mass transport in the regular grid nodes at the cross-section in Fram Strait (8° W, 8° E). The mooring and reanalysis time series were compared, and the results were visualized.
Conclusions. It is shown that the reanalysis ensemble, on the whole, underestimates the transfer of water and heat volumes calculated using the observation data, by 25 %. The best agreement between the reanalysis products and the calculation results based on the observation data is obtained for the West Spitsbergen Current core which is most completely supplied with the observation data. It is revealed that the ensemble of models describes the observation data variability the best, and the FOAM and CGLO reanalysis – the greater part of temporal variability of the flows calculated by the autonomous buoy station data. The data consistency in the winter period (October – March) is shown to be higher than that in the summer one (April – September). That can be related both to the reanalysis imperfections (ice melt accounting) and the season, namely summer, when the autonomous buoy stations are usually replaced, which can result in additional errors in combining the time series.
402-425
Spatial and temporal variability of a latent heat flux in the northwest Pacific Ocean based on the ERA5 reanalysis data
Abstract
Purpose. The paper is aimed at studying the spatial and temporal variability of a latent heat flux – one of the important components of heat balance in the northwestern Pacific Ocean and the Far Eastern seas based on the ERA5 reanalysis data.
Methods and Results. The ERA5 reanalysis data on a latent heat flux in the area limited by the coordinates 42−60° N and 135–180° E and including the Far Eastern seas and the northwestern part of the Pacific Ocean constituted the material for the study. The array of monthly averages at a quarter-degree spatial resolution was analyzed using the standard statistical methods. The average long-term distributions of latent heat flux values for each month were constructed; the amplitudes and phases of annual and semi-annual harmonics, and the linear trend coefficients were calculated in each spatial cell, and the decomposition was performed using the empirical orthogonal functions. The range of seasonal variations is significant in the zone of warm currents, and it sharply decreases in the northern part of the area under study in the Pacific Ocean as well as in the Okhotsk and Bering seas. The interannual variations are manifested in the quasi-cyclic changes of the envelope based on the maximum values with a period of about 6 years. The unidirectional trends in the interannual latent heat flux variations are weakly shown.
Conclusions. Among the seasonal variations of a latent heat flux, the annual cyclicity is predominant and the most pronounced in the southern part of the northwestern Pacific Ocean (the area influenced by the warm Kuroshio Current) off the Japan Sea coast of the Honshu Island in the Tsushima Current zone. This is conditioned by a significant evaporation increase in these areas during a cold season that, in its turn, is related to a sharper temperature contrast as well as to the impact of a winter monsoon characterized by the strong and stable northwesterly winds bringing dry, cold air from the continent. In a warm period, in some areas of the studied water area, the latent heat flux values are positive that indicates the important role of water vapor condensation in the areas with high cloudiness and in the zones of quasi-stationary upwellings.
426-437
Experimental and field research
Dynamics of nutrients concentration in the Chernaya River waters (Crimean Peninsula) in 2015–2020
Abstract
Purpose. The study is purposed at assessing the intra- and interannual dynamics of nutrients concentration (compounds of inorganic nitrogen, phosphorus and silicon) in the Chernaya River waters.
Methods and Results. The quarterly monitoring data on the water hydrochemical characteristics in the lower reaches of the Chernaya River and in the Chernorechenskoe reservoir obtained by Marine Hydrophysical Institute of RAS in 2015–2020 were used. The data obtained made it possible to study the distribution of inorganic nitrogen, phosphorus and silicon compound concentrations in the Chernaya River waters during the period under study as well as its seasonal and interannual changes. As compared to 2010–2014, the ammonia nitrogen levels in 2015–2020 increased on average by 2.7 times. The mean long-term inorganic nitrogen outflow with the Chernaya River waters was 32.46 t/year in 2010–2014 and 27.8 t/year in 2015–2020, phosphorus and silicon – 0.23 and 57.93 t/year in 2010–2014 and 0.18 and 62.21 t/year in 2015–2020, respectively.
Conclusions. An increase in concentrations of all the nutrients under consideration was observed at the stations located near the villages in the Baydar Valley and hence, most susceptible to the anthropogenic impact, as well as in the area of water outlet of the Sevagrosoyuz agricultural firm, that can testify to the inflow of mineral fertilizers to the river waters. Recently the content of nutrients inorganic forms in the Chernaya River waters has increased as compared to the period before 2014, indicating the discussed over the past decade necessity in constructing a sewerage and wastewater treatment system both for the enterprises and the residential development of the Baydar Valley.
438-449
Sea level oscillations in the adjacent bays – Trade Port and Kholmsk-Severny (Sakhalin Island)
Abstract
Purpose. The work is purposed at studying the long-wave processes in the Kholmsk bays and on the adjacent shelf (including the interaction of bays) based on the theoretical concepts and the data of sea level field observations obtained in September, 2022 – May, 2023.
Methods and Results. The observations were performed by three autonomous wave meters ARW-14 K installed in the bays of the Trade Port and Kholmsk-Severny as well as on the shelf at an insignificant distance from the bays. The measurement discreteness was 1 second. The time series both including the tides and without them were studied based on the spectral analysis involving the Kyma program. Within the range of wave periods 1–30 h, the wave processes of a non-tidal origin and with the periods 1.6–6.7 h were revealed. They can be attributed to the shelf seiches, the Poincaré waves or the Tatar Strait seiches. Spectral analysis in the period range 1–10 min has shown the presence of seiches with the periods 1.83–8.17 min in the Trade Port Bay and those with the periods 1.32–8.65 min in the Kholmsk-Severny Bay.
Conclusions. It is established that in course of the whole series of field observations, the coupled oscillations at the periods ~ 8 min took place in the above-mentioned bays. These oscillations correspond to the Helmholtz mode of the Kholmsk-Severny Bay. They are induced in this bay and then, due to interaction, transferred to the Trade Port Bay. At different time points they had both in-phase and anti-phase spatial structures. During the periods of high eigen modes the interaction between the bays was not detected. Besides, the spectral analysis of sea level oscillations under study made it possible to reveal the beats with a period 4.82 h (289.2 min), resulting from the interaction of modes with the close periods equal to 8.17 and 8.65 min. The stated facts as well as the correspondence of the distance between the bays’ inlets to the earlier proposed interaction condition criterion allow us to assert that the coupled oscillations are present in two adjacent bays – Kholmsk-Severny and Trade Port.
450-468
Mathematical modeling of marine systems
Resuspension of bottom sediments in a shallow lagoon by currents and waves based on the numerical modeling data (using the example of Sivash Bay, the Sea of Azov)
Abstract
Purpose. The work is purposed at studying the intensity of resuspension of silty bottom sediments in Eastern Sivash Bay (the Sea of Azov) during an extreme storm, as well as at assessing the contribution of currents and wind waves to the resuspension processes.
Methods and Results. The current fields are calculated using a three-dimensional σ-coordinate water circulation model of the POM type supplemented with a block of silty sediments resuspension. The SWAN spectral model is applied to calculate wind waves. In both models a rectangular computational grid with the horizontal resolution 300 m is involved. The ERA-Interim atmospheric reanalysis data corresponding to the extreme storm situation in November 10–13, 2007 are used as a forcing. The performed calculations constituted a base for analyzing the structure of the fields of waves, currents, bottom shear stresses and suspended matter concentration in Eastern Sivash for different phases of the storm. A technique for assessing the resuspension model sensitivity to the variations in the input parameter values is proposed.
Conclusions. The applied resuspension model is most sensitive to the variations in the parameter values that condition intensity of the silt particles vertical flow from the basin bottom. During the period of the storm maximum development, conditions for forming resuspension zones arise on 80 % of the total area of Eastern Sivash Bay. If, while modeling, the contribution of the waves is not taken into account, the total area of resuspension is reduced by four times. This fact testifies to a decisive contribution of the bottom wave stresses in formation of the resuspension zones in bottom sediments in the bay.
469-488